The reduction in greenhouse gas emissions from transportation is one of the major challenges which vehicle manufacturers find themselves facing today. The tire constitutes a significant source of progress, by means of a reduction in the rolling resistance, since this has a direct impact on the vehicle fuel consumption. Some notable advances have been obtained, as is witnessed, for example, by the great success of the Energy™ Saver tire commercialized by Michelin. The technology used makes it possible to save close to 0.2 l of fuel per 100 km in mixed cycle, which corresponds to a reduction of close to 4 g of CO2 per km, or about one ton of CO2 not emitted into the atmosphere during the life of a vehicle.
Considering the foreseeable increase in the price of oil and the ever-increasing ecological awareness of consumers, it is nevertheless necessary to continue the efforts that aim to reduce the rolling resistance of tires.
The assembly formed by the bead and the radially inner part of the sidewall of a tire is among the components of the tire whose structure has a very marked repercussion on the rolling resistance of the tire. It has a multiple role: it takes up the stresses of the carcass reinforcement and transmits the loads to which the tire is subjected from the sidewall to the rim. Its influence on the road-holding of the tire is considerable, especially when the tire is highly loaded. All of these functions are customarily provided by the combination of a reinforcement (comprising the bead wire and the turn-up of the carcass reinforcement around it) and of a “bead filler” made of a rubber compound. The compromise between the rigidity to be achieved, in particular for the guidance of the crown, and the expected endurance generally leads to choosing a certain trajectory of the carcass reinforcement and to using a voluminous (high and/or thick) and rigid bead filler. Unfortunately, this geometry entails a high hysteretic loss, especially at the bead filler. In a radially outer region remote from the bead wire, the rigidifying effect provided by the bead wire and the turn-up of the carcass reinforcement is reduced. In order to obtain sufficient rigidification in this region, the bead filler has to be even more voluminous, which results in an even greater hysteretic loss.